1. Field of the Invention
The present invention relates to a liquid crystal module suitable for use in portable terminal devices such as mobile telephones and PDAs (personal digital assistants). More particularly, the present invention relates to a liquid crystal module suitable for use as a double-sided display module that allows display on both one and another side of a portable terminal device.
2. Description of Related Art
In recent years, portable terminal devices such as mobile telephones and PDAs have been widely available. Among these devices, mobile telephones, in particular, have become indispensable in our daily life because they provide not only their original telephone capabilities but also other capabilities such as digital camera capabilities and various Internet connection capabilities for e-mail, information searches, navigation, etc.
While mobile telephones are given increasingly high functionality in this way, on the hardware side also, increasingly high degrees of user-friendliness, light-weight and portability have been sought, resulting in development and commercialization of a wide variety of mobile telephones. For example, straight-type mobile telephones common in the past have now been largely superseded by flip-type mobile telephones popular these days.
Less recent models of flip-type mobile telephones were designed to be used in their unfolded state, and it is in this state that they display information. Thus, only one screen is needed for displaying information, and hence, among them, single-screen type mobile telephones are common. By contrast, more recent models of flip-type mobile telephones have come to be increasingly designed to display simple information, such as the caller's name and the current time even in their folded state. Hence, among them, double-screen type mobile telephones provided additionally with a subscreen are common.
As an example of a display module used in such a double-screen type mobile telephone, there is disclosed in patent document 1 listed below a double-sided display liquid crystal module.
FIG. 3 is an exploded perspective view of the double-sided display liquid crystal module disclosed in patent document 1. This double-sided display liquid crystal module is composed of: a main liquid crystal panel 71 that is used as a main display screen in a double-screen type mobile telephone; a holder 72 for holding the main liquid crystal panel 71; a backlight 73 made up of a light guide plate, an optical sheet and other components; a flexible substrate 74; and a sub liquid crystal panel 76 that is used as a subscreen in the double-screen type mobile telephone.
Disadvantageously, however, if the double-sided display liquid crystal module described above is, as it is, housed in the display housing of a mobile telephone, the flexible substrate 74, which is simply placed on the backlight 73, remains completely exposed. Thus, the circuit pattern formed on the flexible substrate 74 and the circuit components mounted thereon are prone to collect dust and the like, and may even be damaged under an impact.
As an improvement, there is disclosed in patent document 2 listed below a liquid crystal module structured as follows. In this liquid crystal module, a main liquid crystal panel located in an upper part thereof and a flexible substrate located on the back side of the main liquid crystal panel are covered from below by a back case formed of a metal plate; the back case has an opening formed therein that corresponds to a sub liquid crystal panel, and the sub liquid crystal panel is directly arranged from below so as to close the opening.
Patent document 1: JP-A-2003-330377 (FIG. 2; paragraphs 0006, 0007 and 0032 to 0034)
Patent document 2: JP-A-2003-207801 (FIG. 3; paragraphs 0013 to 0019)
As compared with the liquid crystal module disclosed in patent document 1, where the flexible substrate is exposed inside the mobile telephone, the liquid crystal module disclosed in patent document 2 is suitable for use as a liquid crystal module in a mobile telephone for the following reasons, among others: in mobile telephones, which are carried around by users and used under various environments, the flexible substrate can be protected by the back case; the back case formed of metal can enhance the strength of the double-sided display liquid crystal module; the metallic back case can shield the liquid crystal module from the noise that is emitted from inside and outside the liquid crystal module.
Inconveniently, however, with a back case formed of a metal plate as disclosed in patent document 2, it is difficult to keep its surface flat. If the back case is insufficiently flat around the opening where the sub liquid crystal panel is directly fitted, it is impossible to stably fit the sub liquid crystal panel therein. To be sure, the sub liquid crystal panel and the back case are fixed together with double-sided tape, adhesive or the like, but even then, if the back case is severely distorted, insufficient adhesion results.
Moreover, with a back case formed of a metal plate, when it is worked on, it is highly likely to form burrs around the opening. Such burrs scratch and damage the sub liquid crystal panel when it is fitted.
Furthermore, since the back case is formed of a single metal plate, when, for example, the double-sided display liquid crystal module is distorted under an impact or the like, the distortion in the back case, to which the sub liquid crystal panel is integrally fitted, passes on directly to the sub liquid crystal panel, and thus the sub liquid crystal panel is highly likely to be broken or otherwise damaged.
As portable terminal devices such as mobile telephones, in particular, are made increasingly compact and slim, the disadvantages described above continue to grow in double-sided display liquid crystal modules.
It is therefore an object of the present invention to provide a compact double-sided display liquid crystal module in which the above-mentioned disadvantages encountered when a sub liquid crystal panel is fitted in a metallic back case have been overcome to realize an optimal double-sided display liquid crystal module used in a portable terminal device.